Cylindrical convergence electrode with shields affixed to inner cylinder walls



3,513,479 CYLINDRICAL CONVERGENCE ELECTRODE WITH SHIELDS AFFIXED S L was N m m .N m H 0 mm J RJ H mm i u IF 0 T May 19, 1970 I NVENTOR fiy/f. fa/Emma,

ATTORNEY United States Patent CYLINDRICAL CONVERGENCE ELECTRODE WITH SHIELDS AFFIXED TO INNER CYL- INDER WALLS Jay H. Johnson, Owensboro, Ky., assignor to Kentucky Electronics, Inc., Owensboro, Ky., a corporation of Delaware Continuation-impart of application Ser. No. 633,822, Apr. 26, 1967. This application Jan. 3, 1969, Ser.

rm. Cl. H01j 29/46 US. Cl. 313-84 2 Claims ABSTRACT OF THE DISCLOSURE A cylindrical convergence cup electrode for a three gun color picture tube has three internally mounted Y-shaped shield inserts of magnetic material afiixed to the inner cylinder wall.

This application is a continuation-in-part application of the copending application Ser. No. 633,822 filed Apr. 26, 1967 which is now US. Pat. 3,441,769, issued Apr. 29, 1969.

This invention relates to electrodes for controlling a beam within a cathode ray tube, and more particularly, it relates to a convergence cup electrode for three beam color television tubes.

Basically, this convergence cup electrode is a cup-like electrode of generally cylindrical shape of a thin-walled non-magnetic metal. Inside the cup is a generally Y-shaped magnetic shield dividing the interior of the cylinder into three substantially equal compartments. A set of two magnetic pole pieces protrude from the outside through two slots in each compartment to straddle an aperture in the closed cup bottom which passes an electron beam. Snubber springs are aflixed to extend generally outwardly from the electrode to press against the inside surface of the glass neck of the cathode ray tube for centering the gun therein. The pole pieces have flanges adjacent the outer Walls of the electrode and near the glass neck of the tube to communicate with convergence magnets located outside the tube envelope.

In constructing this convergence cup assembly, great difliculty has been encountered in holding the roundness of the convergence cup cylinder. It has been found that in punching six pole piece slots and three shield slots through the electrode walls, the cylindrical shape may be distorted out of tolerance.

It has been customary to nick or slot the top edge of a convergence cylinder at three positions about the periphery in order to extend a flange on the Y-shaped shields through the cylinder walls for welding onto the outer cylinder surface. This procedure has long been customary in commercial practice despite the many problems it produces. The cost and maintenance of dies that are needed to punch through stainless steel convergence cup walls is significant. The punching technique is complicated seriously by the roundness of the walls that tends to deflect dies and make precise positioning of slots difficult, to say nothing of excessive die wear.

Furthermore roundness acceptance tolerances of a convergence cup are strict, and any punching or slotting, particularly at the rim edge of a cup tends to misshape the cup and cause out of roundness. Also punched slots provide surfaces which may develop burrs or sharp edges subject to corona discharge and defective operation in the high voltage environment of cathode ray tube electrodes. Such slots are usually inaccessible to elfective tumbling and deburring operations even if the cost of this additional step can be borne.

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In spite of all these deficiencies, cathode ray tube color picture gun assemblies have for the past decade consistently mounted the V-shaped convergence shields by extending flanges through a slot in the cylinder walls so that they could be welded on the outside of the cup. Perhaps in this critical art subject to defect when a minor change is made that will tend to disturb the electron beam characteristics or voltage distribution, there has been a reluctance to put a welded surface inside the electrode cup.

It is therefore an object of this invention to provide a convergence cup electrode structure resolving these deficiencies of the prior art.

Another object of the invention is to provide convergence cup electrode assemblies which can be held to precise roundness tolerance during manufacture.

It has been discovered in accordance with this invention that the convergence cup may be made more precisely at less cost with structure successfully operating in the critical environment of a color picture tube gun exposed to high voltages for shaping, controlling and directing an electron beam with precision over a large range of conditions. Thus, the punched slots in the convergence cup at the rim edge are avoided to thereby provide better roundness of the convergence cup and to avoid problems caused by burrs and other distortions of the electric field configuration affecting the electron beam. Accordingly the V-shaped shield members are aflixed to the inner walls of the convergence cup cylinder with flanges abutting the walls near the rim at the open end of the cup. The abutted flanges are mounted in a position shielded from the electron beam by the magnetic convergence pole pieces to prevent any danger of distorting the beam with distorted inner cup wall surfaces caused by the welding or flange structure.

These and other aspects and objectives of the invention are related throughout the following detailed description which refers to the single figure in the accompanying drawing, which shows a top view of a convergence cup assembly.

As seen from the drawing, the convergence cup may be a deep drawn cylinder having a closed bottom 10. This cup has thin side walls of non-magnetic metal such as stainless steel and may have the upper rim 14 flanged outwardly. Slots 15, 16 extend through the cup walls defining the limits of three separate compartments 18, 19, 20 through which an electron beam is passed.

Two magnetic pole pieces 30, 31 extend through slots 15, 16 into each compartment 18, 19, 20 to straddle apertures 32, 33, 34 which permit the three separate electron beams of a color picture tube to pass through the convergence cup electrode. The flanges 8 on the pole pieces 30, 31 abut the outer walls of the cylinder to extend near the inner wall of the glass neck of the tube 35 about which a conventional convergence magnet array (not shown) is placed to communicate with the pole pieces 30, 31 at each compartment.

Three V-shaped magnetic shield members 23, 24 and 25 extend radially from their common apex to the center 26 of the cup to the cylinder walls forming three substantially equal compartments in the cup to further isolate the three beam compartments within the convergence cup assembly. These shields 23, 24, 25 are wholly contained within the cup and extend substantially to the bottom of the cup. They are spot welded to the inner side walls of the cylinder near the upper rim 14 by means of flanges 21, 22 bent from the plane of each shield to extend cir cumferentially adjacent the inner surface of the cylinder toward the magnetic pole pieces 30, 31. Any possible Weld spots or disturbed magnetic or electric field patterns left inside the convergence cup by this mounting structure are shielded from the beam, which passes through the apertures 32, 33 and 34, by means of the intervening pole pieces 30, 31.

Thus it has been found in practice that this convergence cup construction provided by this invention afiords improved cathode ray picture tube performance, yet is less expensive to manufacture than former structure, thereby leading to widespread commercial use.

What is claimed is:

1. A convergence cup electrode assembly for positioning in the neck portion of a multiple-beam color television cathode ray tube comprising in combination, a hollow cylindrical thin-walled cup electrode body of nonmagnetic material having a partially closed bottom and open top, shield means of magnetic material wholly contained inside said cup and extending radially from the center of the cup to the cylinder wall to divide the cylinder into compartments and having flanges extending circumferentially adjacent the inner surface of the cylinder and afiixed thereto, apertures defined in said closed bottom for passing respective beams axially through each of said compartments, a pair of magnetic pole pieces for each beam, and aperture means disposed in the walls of said cylinder in each compartment for receiving two magnetic pole pieces spaced apart and straddling the respective axial beam paths, wherein the magnetic pole pieces extend into said compartment at a position between said axial beam path and said flanges and are bent over to provide a flange conforming to the outer wall surface of said cup electrode.

2. An electrode as defined in claim 1 wherein the shield means comprise three V-shaped members meeting at an apex at the center of said cup to form three substantially equal compartments.

References Cited UNITED STATES PATENTS 7/1961 Hughes 3l370 5/1967 Fiore 313-70 US. Cl. X.R. 313356 

